d.polar(1)

1d.polar(1)                    Grass User's Manual                   d.polar(1)
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NAME

6       d.polar   -  Draws  polar  diagram  of angle map such as aspect or flow
7       directions
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KEYWORDS

10       display, diagram
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SYNOPSIS

13       d.polar
14       d.polar help
15       d.polar  [-x]  map=name   [undef=float]    [eps=string]     [--verbose]
16       [--quiet]
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18   Flags:
19       -x
20           Plot using Xgraph
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22       --verbose
23           Verbose module output
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25       --quiet
26           Quiet module output
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28   Parameters:
29       map=name
30           Name of raster angle map
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32       undef=float
33           Pixel value to be interpreted as undefined (different from NULL)
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35       eps=string
36           Name of optional EPS output file
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DESCRIPTION

39       d.polar  calculates and displays a polar diagram of an angle raster map
40       such as aspect, wind direction, or flow.  The input angle map  orienta‐
41       tion must be counter-clockwise (CCW) from east, and the angle map units
42       must be degrees. This refers  to  the  standard  orientation  of  GRASS
43       (e.g., see r.slope.aspect).
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45       The radius of the outer circle is defined by the total number of pixels
46       in the map. If the polar diagram does not reach the  outer  circle,  no
47       data (NULL) pixels were found in the map.
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49       The  vector in the diagram indicates a prevailing direction, its length
50       the strength of such direction. In case all angle vectors are  oriented
51       along the same direction, the length for the vector is maximal (in fact
52       it is equal to length of the most populated bin of the underlying  his‐
53       togram).
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55       As  a side effect, the quality of the angle map can be derived from the
56       diagram. Strong spikes  may  indicate  an  over-representation  of  the
57       related angle(s) which happens in particular if integer maps are used.
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NOTES

60       If  the eps parameter is used, the diagram is generated as EPS file. If
61       the -x flag is used xgraph is  lauched.   Otherwise  d.polar  will  use
62       d.graph to draw the plot in the current display frame.
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64       If  d.polar  is  used on an aspect map generated by r.slope.aspect, the
65       undef parameter should be set to 0 to distinguish NO DATA (NULL)  areas
66       from areas where aspect is undefined (i.e. flat areas).
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68       Polar diagram of aspect map
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EXAMPLE

71       In  this  example,  the  polar diagram of the 'aspect' angle map in the
72       Spearfish location is generated:
73       d.polar aspect
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XGRAPH REQUIREMENT

80       Xgraph must be installed for the -x flag to function.
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AUTHORS

83       Markus Neteler, ITC-irst, Italy
84       Bruno Caprile, ITC-irst, Italy
85       Hamish Bowman, Otago University, New Zealand
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87       Last changed: $Date: 2006-10-30 14:34:00 +0100 (Mon, 30 Oct 2006) $
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89       Full index
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91       © 2003-2008 GRASS Development Team
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95GRASS 6.3.0                                                         d.polar(1)